Solar Panels

[TopBadger]

I think our generation is vastly helped by having SSW facing roof in the SE of England and we have a 50 deg pitch roof so the panels subtend a larger angle to Sun (which of course is lower in the sky in winter).

We don't have an electric car to trickle charge... so even with me and the missus working at home, and cooking lunch, and doing some energy intensive chores (Washing, Drying) we can't self consume what we generate on a good day and can only store 6.5kWh.

Perhaps I should look into the economics of getting a second battery installed (~£3k), or a hot water battery - I'll admit I've not heard of these.

I moved to Octopus a few days ahead of the install - so yes - will be on their most favorable export tariff (15p/kWh).

[lpm]

By hot water battery I just mean a hot water cylinder. 150 litres of water will store about 8 kWh of electricity (raising temperature from 10 degrees to 55 degrees). Need space for a cylinder, though. Cheaper than an electrical battery, but obviously the stored energy decays.

I'd turn off the gas central heating and buy a couple of £20 fan heaters, leaving them running whenever you'd otherwise be exporting over the next couple of months. Get the fabric of the house hot.

Exporting at 15p seems really good. Negative energy bills all summer?

[dyqik]

By hot water battery I just mean a hot water cylinder. 150 litres of water will store about 8 kWh of electricity (raising temperature from 10 degrees to 55 degrees). Need space for a cylinder, though. Cheaper than an electrical battery, but obviously the stored energy decays.

I'd turn off the gas central heating and buy a couple of £20 fan heaters, leaving them running whenever you'd otherwise be exporting over the next couple of months. Get the fabric of the house hot.

Exporting at 15p seems really good. Negative energy bills all summer?

A couple of minisplit heat pump units would be a good investment vs a battery, probably. Let them take over from gas heating in winter (and they may well be cheaper than gas even on regular rate electricity at night in 5C weather), and get free AC in summer.

[TopBadger]

Ah - I went looking for Hot Water Battery and thought you were referring to these:

https://sunflowltd.co.uk/sunamp/

Which is a phase change battery... I already have a hot water cylinder (megaflow - like the one in their screenshots which their system would replace).

Perhaps in the interim I should just turn on the immersion heater in the daytime?

ETA - Solar generated 26.3kWh today...!

[dyqik]

Perhaps in the interim I should just turn on the immersion heater in the daytime?

Yep, that's free hot water. And if your hot water tank is somewhere where it leaks heat to the house, free heating.

[lpm]

Those Sunamps are crazy expensive for hot water.

Using the immersion for the next couple of months while throwing away generation seems obvious. 3-4 kWh a day maybe. Probably worth it across the summer as well. Giving up 15p export vs gas heating at 12p (assuming 10p/kWh and 85% boiler efficiency) is similar ballpark, with the enjoyment of knowing it's your own energy and extending the life of the boiler and the CO2 saving.

[IvanV]

Perhaps in the interim I should just turn on the immersion heater in the daytime?

Yep, that's free hot water. And if your hot water tank is somewhere where it leaks heat to the house, free heating.

Managing it requires thought and intervention, and excess cost if you forget to turn it off when the panels aren't generating enough. Also wise to strategically leaving the gas heating off at suitable times, so the water isn't already hot when the sun is available.

You can get a diverter thingy that does some of that for you, but it costs around £500 installed.

[dyqik]

Perhaps in the interim I should just turn on the immersion heater in the daytime?

Yep, that's free hot water. And if your hot water tank is somewhere where it leaks heat to the house, free heating.

Managing it requires thought and intervention, and excess cost if you forget to turn it off when the panels aren't generating enough. Also wise to strategically leaving the gas heating off at suitable times, so the water isn't already hot when the sun is available.

You can get a diverter thingy that does some of that for you, but it costs around £500 installed.

Or you just let the immersion heater run whenever, instead of at night during "cheap rate"electricity. This is because your daytime electricity is actually cheaper than the cheap rate due to the solar panels. Since you tend to use hot water during the day rather than while sleeping, that does everything needed for you

You don't need to turn the gas heating off - the water heater will leak heat anyway, and reduce the amount of time the heating runs for.

[lpm]

Hot water cylinders need to transition to smart. I control mine with an app. And the immersion can be turned on and off remotely, for grid balancing.

[IvanV]

Yep, that's free hot water. And if your hot water tank is somewhere where it leaks heat to the house, free heating.

Managing it requires thought and intervention, and excess cost if you forget to turn it off when the panels aren't generating enough. Also wise to strategically leaving the gas heating off at suitable times, so the water isn't already hot when the sun is available.

You can get a diverter thingy that does some of that for you, but it costs around £500 installed.

Or you just let the immersion heater run whenever, instead of at night during "cheap rate"electricity. This is because your daytime electricity is actually cheaper than the cheap rate due to the solar panels. Since you tend to use hot water during the day rather than while sleeping, that does everything needed for you

You don't need to turn the gas heating off - the water heater will leak heat anyway, and reduce the amount of time the heating runs for.

That assumes you have cheap night rate electricity. Most people in Britain don't. You need to have a large night time load to make it worthwhile.

The point is to try and use your "spill units" to heat water rather than spill onto the grid. During the summer, I would have a lot of spill units. To achieve that, you need to have the water cool enough to absorb that electricity. My hot water tank is very well insulated, and wouldn't absorb much electricity during the day unless I had deliberately avoided heating it during dim times, whether by electricity or gas if substantial power is later to arrive. It is especially important not to have the gas/mains electricity on at the point you have your morning shower, if there is solar power to retrieve that loss of heat.

[dyqik]

Managing it requires thought and intervention, and excess cost if you forget to turn it off when the panels aren't generating enough. Also wise to strategically leaving the gas heating off at suitable times, so the water isn't already hot when the sun is available.

You can get a diverter thingy that does some of that for you, but it costs around £500 installed.

Or you just let the immersion heater run whenever, instead of at night during "cheap rate"electricity. This is because your daytime electricity is actually cheaper than the cheap rate due to the solar panels. Since you tend to use hot water during the day rather than while sleeping, that does everything needed for you

You don't need to turn the gas heating off - the water heater will leak heat anyway, and reduce the amount of time the heating runs for.

That assumes you have cheap night rate electricity. Most people in Britain don't. You need to have a large night time load to make it worthwhile.

The point is to try and use your "spill units" to heat water rather than spill onto the grid. During the summer, I would have a lot of spill units. To achieve that, you need to have the water cool enough to absorb that electricity. My hot water tank is very well insulated, and wouldn't absorb much electricity during the day unless I had deliberately avoided heating it during dim times, whether by electricity or gas if substantial power is later to arrive. It is especially important not to have the gas/mains electricity on at the point you have your morning shower, if there is solar power to retrieve that loss of heat.

If you don't have cheap rate electricity at night, then you are already using your immersion heater in the day, and don't need to do anything.

Showering in the morning* means that the hot water used is replaced during the morning, when the sun is at least rising, if not up.


*which is a weird habit if you think about it - I shower at night to wash off the dirt and sweat of the day before getting into bed, rather than sleeping in my own filth.

[IvanV]

If you don't have cheap rate electricity at night, then you are already using your immersion heater in the day, and don't need to do anything.

I'm not using it at all. It is there for back-up purposes only, when my gas boiler breaks down.

[IvanV]

Showering in the morning* means that the hot water used is replaced during the morning, when the sun is at least rising, if not up.

If you have a shower around dawn, you will pay to reheat the water, either because the gas will do it first, or because you aren't generating enough solar power until a couple of hours later. You have to leave these systems off, and turn the immersion heater on only when you are generating enough power to power the immersion heater.

I think my immersion heater is about 1kW. In grim British light, with the 4kW of panels on the roof that the company is proposing to fit, I wouldn't be getting 1kW of power from the sun until the sun was well up, and it wasn't too cloudy. The average capacity factor of solar panels in Britain is 11%. So if we ignore hours of darkness, that's 22% during daylight hours. Clearly it depends on the shape of the distribution, but during over half of daylight hours, I wouldn't be getting enough power from my panels to run the immersion heater. And the mains would be topping it up.

Though I expect to be getting a battery and that will make it easier. In fact, running down the battery before a nice sunny day makes sense.

[TopBadger]

I have a 5kWp system and it was producing 1kWh by 9:40am on a foggy morning today...

Generally, on decent days, I've found the house is solar powered from 9am (from looking at the system logs and also looking at the live feed of my wireless electricity meter... it's often been zero when I get back after dropping the kids off at school).

Yesterday with the battery we were solar powered from 8:45am to 4:20am the next day (this morning)... had the export tariffs been in place yesterday would have been a net 35p spend on imports (because we imported just under 1kWh the whole day).

[lpm]

Showering in the morning* means that the hot water used is replaced during the morning, when the sun is at least rising, if not up.

If you have a shower around dawn, you will pay to reheat the water, either because the gas will do it first, or because you aren't generating enough solar power until a couple of hours later. You have to leave these systems off, and turn the immersion heater on only when you are generating enough power to power the immersion heater.

I think my immersion heater is about 1kW. In grim British light, with the 4kW of panels on the roof that the company is proposing to fit, I wouldn't be getting 1kW of power from the sun until the sun was well up, and it wasn't too cloudy. The average capacity factor of solar panels in Britain is 11%. So if we ignore hours of darkness, that's 22% during daylight hours. Clearly it depends on the shape of the distribution, but during over half of daylight hours, I wouldn't be getting enough power from my panels to run the immersion heater. And the mains would be topping it up.

Though I expect to be getting a battery and that will make it easier. In fact, running down the battery before a nice sunny day makes sense.

I think you're only looking at pieces. It works when it comes together as a whole.

Modern hot water cylinders lose approx 1 kWh per day. So you can charge it with up to 8 kWh of energy at any time of day or night you choose. You don't use a couple of kWh on a shower and then top it up again, you wait till the next recharge session.

The standard method is to flip between seasons - in summer store energy in the day from PV, in winter do it overnight with cheap electricity. The minute you get a battery - home, car or water - the day/night Time Of Use tariffs come into play. You only need to beat 30% night time usage for TOU to become cheaper than flat rate.

[lpm]

The next Ripple is going to be solar.

https://www.youtube.com/watch?v=y1W2ft1WCzo

Details and full prospectus in a couple of weeks.

[bjn]

The next Ripple is going to be solar.

https://www.youtube.com/watch?v=y1W2ft1WCzo

Details and full prospectus in a couple of weeks.

Done.

Oooooh, much cheaper than getting it put on my roof.

I need to start looking at heat pumps soon.

[lpm]

But also a lot lower return than getting it on your roof.

Will be interesting to see the detail. My guess it'll be a third the price of an install but a third of the return

[bjn]

It all depends on the numbers, but getting undiscounted credits in periods of overproduction may be better than an FIT or pumping the electrons into a battery.

[lpm]

She says £2,600 for average home, and digging into the old stuff they say their average home metric is 2,900 kWh p.a.

Kirk Hill was £1,714 for 2,900 kWh. Or after a year of 10% inflation, £1,885 in today's terms. This makes it look a lot more expensive than onshore wind.

The price of home solar installation these days would be the equivalent of £6,000 to £7,000. So a 2.5x multiple rather than 3x. That home solar would save about £560 a year, about 19p per kWh. Which implies Ripple would need to deliver at about 8p per kWh net of running costs to match the 2.5x build cost ratio.

[nekomatic]

I need to start looking at heat pumps soon.

We had Octopus in yesterday to survey for a heat pump, now waiting for the quote. May not go ahead in any case because where the outdoor unit would have to go isn’t great and the tickbox-driven rules for the subsidy apparently require some pointless and awkward radiator upgrades, but they were very happy to come and do the assessment for free.

[lpm]

Got a Ripple email. Solar park in Devon.

Looks too expensive but will add a bit.

[TopBadger]

I'm really looking forward to getting my export set up - the time it takes to do this is a joke. System installed end of Jan and I'm still not being paid for my exports.

[bjn]

Got a Ripple email. Solar park in Devon.

Looks too expensive but will add a bit.

I have the email and previously put down the £25 deposit. They are estimating a 5% return over 40 years (I’d be 98 by the end of that!). I’m also already down for Kirk Hill to meet most of my needs, but I may top up slightly on the solar farm. Minimum is £25, so I’ll be down for that anyway. Humming and haaaing about how big a share to buy.

[lpm]

Haven't had time to run the numbers.

But it's more like buying an annuity than making an investment. A 40 year annuity is very expensive. An inflation-linked annuity that can be inherited by a spouse even more expensive. An annuity that's index linked to wholesale electricity prices doesn't exist, but is quite attractive.

Looks like we pay £3,000 to buy a 40-year annuity with £170 income p.a.. 5.6%. I think that's OK. A normal inflation-linked annuity would cost that, I believe.